Sticky cleaner for removing organic dirt

ABSTRACT

Provided is a sticky cleaner that can easily remove organic dirt adsorbed on a surface of an article with greater dirt-removing workability. The sticky cleaner provided by the present invention is used for removing organic dirt adsorbed on a flat surface of an article. The sticky cleaner comprises a dirt-collecting member that collects the organic dirt as it makes contact with the flat surface. In the dirt-collecting member, the part to make contact with the surface is formed with a PSA. The surface-contacting part of the dirt-collecting member exhibits an adhesive strength of less than 1 N/25 mm as a measured value based on the 180° peel test specified in JIS Z0237.

TECHNICAL FIELD

The present invention relates to a sticky cleaner used for removingorganic dirt. In particular, it relates to a sticky cleaner used forremoving sebum and other organic dirt from a flat surface (e.g. a touchpanel display/input screen) in a portable device such as a tabletterminal, smartphone and the Eke. The present application claimspriority based on Japanese Patent Application No. 2013-012473 filed onJan. 25, 2013 and the entire contents thereof are incorporated herein byreference.

BACKGROUND ART

A display typically formed of a liquid crystal panel or an organic ELpanel is placed on a flat surface in a portable device, for instance, aportable personal computer (PC) such as notebook PCs, etc.; tabletterminal such as electronic books, etc.; mobile phone such assmartphones, etc.; mobile gaming device; various types of PDA (personaldigital assistant); and the Eke. These portable devices are carried andused on a daily basis, and thus easily attract dust and organic dirtsuch as finger marks, cosmetics and sebum. In particular, recentlywide-spread touch-screen portable devices are operated with a directfinger touch by a user to the display/input portion in which the displayfunctions also as an input device, and thus are more likely to attractorganic dirt such as finger marks, sebum, etc. Not just these portabledevices, but also show window glass, glass tables, showcases and thelike have flat surfaces. The organic dirt adsorbed on their surfacesdegrades their exteriors, making them unsightly.

As means to remove organic dirt adsorbed on the display, a wipe (wastecloth) made of paper, woven fabric or non-woven fabric is used. Forinstance, when the dirt includes an oily component such as sebum and thelike, wiping off dirt with a wipe is not necessarily easy to carry out,possibly spreading the dirt depending on how it is done or requiringmultiple times of wiping, and so on. Dirt gradually accumulates withcontinuous use, requiring regular cleaning or a replacement with a newpiece, which can be troublesome. Alternatively, there is a means whereorganic dirt is removed by wiping the surface with a suitable material(e.g. sponge or gauze) containing a suitable detergent (e.g. see PatentDocument 1). However, not only is careful handling of the detergentnecessary, but residual detergent can even affect the surface. Thismethod thus requires elimination of the detergent and thus is notadvantageous in terms of workability.

CITATION LIST Patent Literature

[Patent Document 1] Japanese Patent Application Publication No.2009-503161

[Patent Document 2] Japanese Patent Application Publication No.2004-237023

SUMMARY OF INVENTION Technical Problem

The present invention has been made to solve the conventional problem.An objective thereof is to provide a sticky cleaner that can easilyremove organic dirt adsorbed on a surface of an article with greaterdirt-removing workability.

Solution to Problem

To achieve the objective, the present invention provides a stickycleaner used for removing organic dirt adsorbed on a flat surface of anarticle. The sticky cleaner comprises a dirt-collecting member thatcollects the organic dirt as it makes contact with the flat surface. Inthe dirt-collecting member, the part to make contact with the surface isformed with a pressure-sensitive adhesive (PSA). The surface-contactingpart of the dirt-collecting member exhibits an adhesive strength of lessthan 1 N/25 mm as a measured value based on the 180° peel test specifiedby JIS Z0237.

According to a sticky cleaner (dirt remover) having such a constitution,by allowing the PSA constituting the dirt-collecting member to makecontact with a flat surface of an article, organic dirt (e.g. fingermarks and sebum residue of a person or cosmetics) adsorbed on thesurface can be collected and easily removed therefrom. Thesurface-contacting part of the dirt-collecting member exhibits anadhesive strength of less than 1 N/25 mm as a measured value based onthe 180° peel test specified by JIS Z0237. This means that thedirt-collecting member is easily releasable. Accordingly, when thecleaner is operated on a flat surface of an article (e.g. moved on thesurface or taken away from the surface), it requires little force,thereby providing excellent dirt-removing workability. Furthermore, evenwhen the article's surface (e.g. tablet terminal's display) is coveredwith removable protection film, because of the easy-release nature, itcan clean the surface without removing the protection film (in otherwords, while keeping the article surface covered with the protectionfilm). In addition, despite such easy-release nature, it cansufficiently remove organic dirt. As described above, the organic dirtincludes sebum from the skin, and as evident from this, it may includeinorganic substances such as sodium and potassium as well as theirsalts, etc.

In a preferable embodiment of the sticky cleaner disclosed herein, thesurface-contacting part of the dirt-collecting member exhibits anadhesive strength of 0.01 N/25 mm to 0.5 N/25 mm as a measured valuebased on the 180° peel test specified in JIS Z0237. Such an easy-releasecleaner can sufficiently remove organic dirt while providing greaterdirt-removing workability.

In a preferable embodiment, the sticky cleaner disclosed hereincomprises a cylindrical rolling member and the dirt-collecting member isarranged along the lateral surface of the rolling member. According to acleaner having such a constitution, when the rolling member is allowedto rotate in the circumferential direction of the cylinder, thedirt-collecting member on the lateral surface can efficiently removeorganic dirt on the flat surface. Since the dirt-collecting member canbe released easily, the peel resistance during the rotation is low,leading to excellent dirt-removing workability.

In a preferable embodiment, the sticky cleaner disclosed herein furthercomprises a grip member that supports the rolling member in a freelyrotatable manner. With this constitution, a user can hold the gripmember and rotate the rolling member to efficiently remove organic dirtfrom the flat surface.

In a preferable embodiment of the sticky cleaner disclosed herein, thedirt-collecting member is constituted as an adhesively single-faced PSAsheet comprising a sheet of support substrate and a PSA layer placedabove the support substrate, and the single-faced PSA sheet is woundwith the PSA layer on the outside to form a PSA sheet roll. With asticky cleaner having such a constitution, the lateral surface of thePSA sheet roll can be used to remove dirt from a flat surface. Inaccordance with the usage and the amount of dirt caught on the PSAlayer, the lateral surface used for dirt removal can be eliminated from(typically peeled off) the roll to expose an unused section of the PSAlayer on the lateral surface. In other words, the PSA layer can beeasily refreshed to expose an unused section to the outer surface.Accordingly, a desirable level of dirt-removing ability can beconstantly maintained.

Preferably, the PSA sheet roll disclosed herein is constituted to deterrail drawing phenomenon. Rail drawing herein refers to a phenomenon suchthat when the sheet roll is rolled (rotated) reversely to the windingdirection (typically in a direction in which the wound single-faced PSAsheet is peeled) on the surface to be cleaned (a flat surface of anarticle), a band of the PSA sheet stays adsorbed on the surface to becleaned, beginning from the outer circumferential end of the roll.Reduced occurrence of rail drawing allows for stress-free, smoothrotation of the roll on the flat surface, leading to great usability. Inaddition, it can also prevent wasteful use of the PSA sheet due to theoccurrence of rail drawing (i.e. waste of the sheet due to unintentionaladhesion of the PSA sheet to the surface).

In a preferable embodiment of the sticky cleaner disclosed herein, thePSA layer comprises an acrylic polymer at a ratio of 50% by mass orhigher. The use of the acrylic polymer as the PSA can preferably bringabout both removal of organic dirt and easy release. The acrylic polymeris preferably a crosslinked acrylic polymer. This further increases theease of release. Alternatively, it is preferable that the acrylicpolymer is a thermoplastic acrylic polymer. This facilitates formationof PSA layers.

Preferably, the PSA layer further comprises a plasticizer. The inclusionof the plasticizer can lighten the release and lead to greaterdirt-removing workability. Even when the dirt-collecting ability isreduced as a result of use, it preferably exhibits an effect ofregaining its dirt-collecting ability in relatively short time (e.g.several minutes or several hours) (dirt-collecting ability recoveryeffect).

In a preferable embodiment, the sticky cleaner disclosed herein is usedfor removing human sebum dirt as the organic dirt. The sticky cleanerhaving the prescribed constitution disclosed herein effectively removeshuman sebum dirt despite the easy-release nature. This has been madepossible for the first time through the studies by the presentinventors. The sticky cleaner is particularly suitable for removinghuman sebum dirt.

In a preferable embodiment of the sticky cleaner disclosed herein, thearticle is a portable device having a glass or synthetic resin displayon the flat surface. The portable device is carried and used on a dailybasis and is likely to attract organic dirt such as sebum. Inparticular, a portable device having a touch panel display(display/input member) is operated with a direct finger touch to thedisplay/input portion, and thus is more likely to attract organic dirtsuch as finger marks, cosmetics, sebum dirt, etc. The sticky cleanerdisclosed herein can easily remove such organic dirt; and therefore, itis particularly preferably used for removing dirt from a portable devicehaving a display as described above (e.g. a touch panel display). Stickycleaners have been conventionally used (e.g. see Patent Document 2).However, conventional roller cleaners are used for cleaning floors andcarpets, but not intended for cleaning flat surfaces (e.g. touch paneldisplay/input portions) of portable devices (e.g. tablet terminals andsmartphones) as described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a front view schematically illustrating the sticky cleaneraccording to an embodiment.

FIG. 2 shows a side view schematically illustrating the sticky cleaneraccording to an embodiment.

FIG. 3 shows a cross-sectional view schematically illustrating thedirt-collecting member constituting the sticky cleaner according to anembodiment.

FIG. 4 shows a perspective view schematically illustrating an example ofusage of the sticky cleaner according to an embodiment.

FIG. 5 shows a diagram schematically illustrating the mechanism ofdirt-removing ability recovery effect of the sticky cleaner according toan embodiment.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention are described below.Matters necessary to practice this invention other than thosespecifically referred to in this description may be understood as designmatters to a person of ordinary skill in the art based on theconventional art in the pertinent field. The present invention can bepracticed based on the contents disclosed in this description andtechnical common knowledge in the subject field.

The sticky cleaner disclosed herein is different from conventionalsticky cleaners used for cleaning floors and carpets. It is used forremoving organic dirt adsorbed on a flat surface of an article such as aportable device. The article on which the sticky cleaner disclosedherein is used is not particularly limited as long as it has a flatsurface. Examples include show window glass, glass tables, showcases andthe like. As organic dirt adsorbed on their flat surfaces (typicallytransparent glass surfaces) is unsightly, if found any, its quickremoval is desirable. Thus, on their surface, the sticky cleanerdisclosed herein can be preferably used.

Preferable examples of the article on which the sticky cleaner disclosedherein is used include various portable devices. The term portabledevice herein refers to a mobile device having a flat surface at leastpartially on the outside and is not limited to a particular device.Examples include portable devices such as notebook PCs; tablet terminalssuch as electronic books, etc.; smartphones and other mobile phones;mobile gaming devices; PDAs (mobile terminals) such as electronicorganizers, etc.; and the like. Since these are carried and used on adaily basis, they are likely to attract dust and especially organic dirtsuch as finger marks, cosmetics and sebum. Some of these portabledevices have displays such as liquid crystal displays, organic ELdisplays and the like on flat surfaces (typically glass or syntheticresin surfaces). Organic dirt on the displays makes informationdisplayed thereon hard to see, thereby hindering the use. Moreover,depending on the amount of organic dirt adsorbed thereon, it might givea filthy impression. On portable devices having such displays, thesticky cleaner disclosed herein can be preferably used.

In particular, portable devices having touch panel display/inputportions are likely to attract the organic dirt since users directlytouch the displays with fingers. Thus, the sticky cleaner disclosedherein can be preferably used on them. Among them, tablet terminals suchas electronic books and the like have relatively large displays; andtherefore, they are considered as particularly preferable articles onwhich the sticky cleaner is used.

The sticky cleaner according to an embodiment is described below withreference to drawings. As shown in FIGS. 1 and 2, a sticky cleaner (orsimply cleaner, hereinafter) 10 comprises a cylindrical holding member(core) 20 and a PSA sheet roll 30 held on the outer periphery of holdingmember 20. These holding member 20 and PSA sheet roll 30 are assembledto form a cylindrical rolling member. The holding member material is notparticularly limited. A holding member made of a polyolefin or othersynthetic resin as well as paper can be preferably used.

Cleaner 10 further comprises a grip member 40 in a form of a pole thatsupports holding member 20 in a freely rotatable manner. In particular,holding member 20 has a center hole (not shown in the drawings) formedwhere the central axis of the cylinder is located. A terminal section(one end) of grip member 40 is inserted through the center hole, wherebyholding member 20 is installed on grip member 40 in a freely rotatablemanner. To the other end of grip member 40, a handle 42 is attached. Thematerials of grip member and handle are not particularly limited. Forinstance, metal or synthetic resin pieces can be used.

PSA sheet roll 30 in cleaner 10 is formed by winding a PSA sheet 31 thatserves as the dirt-collecting member. In particular, PSA sheet(dirt-collecting member) 31 is constituted as a single-faced PSA sheet31 comprising, as shown in FIG. 3, a support substrate 36 in a form of along sheet (band) and a PSA layer 32 placed on one face 36A of thesupport substrate 36. Single-faced PSA sheet 31 is wound with the PSAlayer 32 on the outside and formed as a PSA sheet roll 30.

With respect to cleaner 10 having a constitution as described above,some applications are now described. As shown in FIG. 4, cleaner 10 isused for removing organic dirt adsorbed on a display 2 of a portabledevice 1. Display 2 in portable device 1 has a flat surface. An operatorplaces cleaner 10 on the display 2 of portable device 1, grip a handle42, and applies a prescribed amount of external force to cleaner 10. Theforce is then transmitted from grip member 40 to holding member 20, andthe PSA layer 32 (a section of the dirt-collecting member that makescontact with the flat surface) placed on the outer periphery of holdingmember 20 rotationally moves on display 2. In FIG. 4, PSA sheet roll 30moves on display 2 in the direction shown by the arrow. During this, thePSA layer 32 collects dust, fine particles, and especially organic dirtsuch as human finger marks, sebum and the like present on the display 2.By this means, cleaning (dirt removal) of display 2 is easily andcertainly accomplished in the rotation direction of PSA sheet roll 30(more specifically, the PSA sheet (dirt-collecting member) 31). Theportable device in this embodiment is a tablet terminal whose display isentirely formed with flat tempered glass such as aluminosilicate glassand the like although it is not limited to this as indicated earlier.

The size of the cylindrical PSA sheet roll is not particularly limited.When it is used on portable devices such as tablet terminals, etc., itsdiameter (which refers to the diameter (outer diameter) before used; thesame applies hereinafter) is preferably 4 mm or larger (e.g. 10 mm orlarger, typically 20 mm or larger). From the standpoint of themaneuverability and portability, the diameter is preferably 50 mm orsmaller (e.g. 35 mm or smaller, typically 30 mm or smaller).

In the PSA sheet roll, the PSA sheet preferably has cut lines (not shownin the drawings) at an interval of approximately the length of thecircumference. The cut lines provide cutting means for efficientlyrefresh the PSA layer surface (outer surface of the dirt-collectingmember) with a reduced cleaning (dirt-removing) ability after thecleaner is used several times. The cut lines can be, for instance, linesof long holes or wavy slits; intermittent slits such as perforation; andthe like. The cut lines are preferably arranged to run across the PSAsheet in the width direction (direction perpendicular to the lengthdirection). Refreshing the lateral surface of the dirt-collecting memberis not limited to the cutting means. For instance, intermittent slitssuch as perforation can be spirally formed in a direction intersectingthe winding direction of the PSA sheet roll (typically, in a directionintersecting the width direction at an angle between 30° and 60°).Alternatively, instead of intermittent slits such as perforation, thePSA sheet constituting the PSA sheet roll may comprise slits (continuouscut lines) at a prescribed interval. In this embodiment, the PSA sheetconstituting the PSA sheet roll is fully cut in advance at theprescribed intervals in the winding direction of the roll. Thus, theouter surface of the PSA sheet roll can be peeled over the length of theprescribed interval to easily refresh the outer surface.

The cleaner 10 can be produced by suitably employing heretofore knowntechniques. For instance, PSA sheet roll 30 of cleaner 10 can befabricated in the same manner as conventional roller cleaners. In otherwords, a PSA composition is applied to the surface 36A of a long sheetof support substrate 36 by various heretofore known coating means andsubsequently allowed to dry to form a PSA layer 32. The PSA sheet 31 iswound around holding member 20 with the PSA layer 32 on the outside toform PSA sheet roll 30 in a form of a roll. A terminal section of gripmember 40 is further attached to holding member 20 in a freely rotatablemanner to construct cleaner 10. The structure of attachment of gripmember 40 to holding member 20 can be similar to those in conventionalroller cleaners and does not characterize the present invention.Accordingly, detailed description is omitted.

The sticky cleaner is not limited to the embodiment above. The stickycleaner may be formed, for instance, solely with a dirt-collectingmember. Examples of such a sticky cleaner include a cleaner formedsolely with a dirt-collecting member in a form of a sphere, column,cylinder, hexahedron (e.g. cuboid), sheet, etc.

In this embodiment, the dirt-collecting member is formed with, but notlimited to, the support substrate and PSA layer. For instance, thedirt-collecting member may be formed solely with a PSA (substrate-freePSA). Alternatively, when the dirt-collecting member has a supportsubstrate, the shape of the support substrate is not particularlylimited. For instance, the dirt-collecting member may have a PSA layeron the outer surface of a spherical support substrate.

In this embodiment, the grip member supports the holding member in afreely rotatable manner, but it is not limited to this. For instance,the grip member may be directly or indirectly joined (connected ordetachably joined) to the dirt-collecting member. In an example of sucha sticky cleaner, a columnar or cuboid PSA body is fastened to one endof a pole-shaped grip member. Alternatively, the grip member may have aflat portion and the dirt-collecting member may be fastened to one faceof the flat portion.

The dirt-collecting member (e.g. PSA sheet) disclosed herein ischaracterized by that the part (e.g. sticky surface) that makes contactwith a flat surface of an article exhibits an adhesive strength of lessthan 1 N/25 mm as a measured value based on the 180° peel test specifiedin JIS Z0237. This means that the dirt-collecting member is easilyreleasable. A cleaner having such an easily releasable dirt-collectingmember requires little force for the dirt-removing operation on thesurface, providing excellent dirt-removing workability. Morespecifically, the cleaner can be moved more smoothly on a flat surfaceof an article and has advantages such that the cleaner can be easilyseparated from the surface after the dirt-removing operation. Even whenthe surface of the article (e.g. display of a tablet terminal) iscovered with removable protection film (e.g. protection film made of asilicone-based or polyester-based synthetic resin, etc.), because of theeasy-release nature, it can clean the surface without removing theprotection film (i.e. while keeping the article surface covered with theprotection film). In this case, the object to be cleaned is the surfaceof the protection film and such a surface is also included in thearticle's flat surface. From the standpoint of the dirt-removingworkability, the adhesive strength is preferably 0.8 N/25 mm or less(e.g. 0.6 N/25 mm or less, typically 0.5 N/25 mm or less) or morepreferably 0.57 N/25 mm or less (e.g. 0.55 N/25 mm or less, typically0.4 N/25 mm or less). From the standpoint of the dirt-collectingability, the adhesive strength is preferably 0.001 N/25 mm or greater(e.g. 0.01 N/25 mm or greater, typically 0.02 N/25 mm or greater) ormore preferably 0.03 N/25 mm or greater (e.g. 0.05 N/25 mm or greater,typically 0.08 N/25 mm or greater).

In particular, the adhesive strength is measured according to thefollowing procedures: The dirt-collecting member (typically a PSA sheet)is cut to a rectangular sheet to prepare a test piece. The test piecepreferably has a length of about 100 mm to 200 mm and a width of about15 mm to 30 mm. When the width is not 25 mm, the value in N/25 mm can bedetermined (by conversion) based on the ratio of actual width to 25 mm.The thickness is not particularly limited. The resulting test piece isadhered over its sticky face (e.g. PSA layer-side surface) to astainless steel (SUS304) plate with a 2 kg roller moved back and forthonce. When the test piece is sticky on each face such as in adouble-faced PSA sheet, etc., it is preferable to back the surfaceopposite the measured surface with a polyethylene terephthalate (PET)film of about 25 μm in thickness. This is stored in an environment at23° C. and 50% RH for 30 minutes. Based on JIS Z0237, using a tensiletester, in an environment at 23° C. and 50% RH, the 180° peel strength(N/25 mm) to SUS is measured. The tensile tester is not particularlylimited and a heretofore known tensile tester can be used. For instance,measurements can be made with trade name “TENSILON” available fromShimadzu Corporation.

The dirt-collecting member (e.g. PSA sheet) disclosed herein may becharacterized by that, instead of or in addition to the 180° peelstrength to SUS, the part (e.g. sticky surface) that comes in contactwith the article's flat surface exhibits a 180° peel strength of lessthan 1 N/25 mm to a glass plate. A cleaner having such an easilyreleasable dirt-collecting member provides excellent dirt-removingworkability. From the standpoint of the dirt-removing workability, theadhesive strength is preferably 0.9 N/25 mm or less (e.g. 0.85 N/25 mmor less, typically 0.5 N/25 mm or less) or more preferably 0.57 N/25 mmor less (e.g. 0.55 N/25 mm or less, typically 0.4 N/25 mm or less). Fromthe standpoint of the dirt-collecting ability, the adhesive strength ispreferably 0.001 N/25 mm or greater (e.g. 0.01 N/25 mm or greater,typically 0.02 N/25 mm or greater) or more preferably 0.03 N/25 mm orgreater (e.g. 0.05 N/25 mm or greater, typically 0.06 N/25 mm orgreater). The 180° peel strength to the glass plate (180° peel strengthto glass) can be measured similarly to the measurement of the 180° peelstrength to SUS except that the glass plate (e.g. a commercial floatglass plate) is used as the adherend.

The dirt-collecting member (e.g. PSA sheet) disclosed herein may becharacterized by that, instead of or in addition to the 180° peelstrength to SUS, the part (e.g. sticky surface) that comes in contactwith the article's flat surface exhibits a 180° peel strength of lessthan 1 N/25 mm to polyethylene terephthalate (PET) film. A cleanerhaving such an easily releasable dirt-collecting member providesexcellent dirt-removing workability. From the standpoint of thedirt-removing workability, the adhesive strength is preferably 0.9 N/25mm or less (e.g. 0.8 N/25 mm or less, typically 0.6 N/25 mm or less) ormore preferably 0.5 N/25 mm or less (e.g. 0.4 N/25 mm or less). From thestandpoint of the dirt-collecting ability, the adhesive strength ispreferably 0.001 N/25 mm or greater (e.g. 0.01 N/25 mm or greater,typically 0.02 N/25 mm or greater). The 180° peel strength to PET film(180° peel strength to PET) can be measured similarly to the measurementof the 180° peel strength to SUS except that PET film is used as theadherend.

When the sticky cleaner disclosed herein has a PSA sheet roll, the PSAsheet roll preferably has balanced adhesive strength (e.g. the measuredvalue based on the 180° peel test) and unwinding force so that theoccurrence of rail drawing is reduced on the article's flat surface(e.g. a surface formed of glass such as aluminosilicate glass orsynthetic resin). The unwinding force herein refers to the forcerequired to pull out the PSA sheet from the PSA sheet roll (i.e.resistive force against unwinding, which can be perceived as theadhesive strength to the back face of the PSA sheet (typically the backface of the support substrate). For instance, when the unwinding forceis excessively low as compared with the adhesive strength, when the PSAsheet roll is rotated on a flat surface, the unwinding force may succumbto the adhesive strength between the PSA sheet (typically the PSA layer)and the surface to cause rail drawing. On the other hand, an excessivelyhigh unwinding force tends to result in unsmooth unwinding of the PSAsheet.

The unwinding force can be assessed as follows. In particular, the PSAsheet roll is set in a prescribed tensile tester. In an environment at atemperature of 23° C. and 50% RH, the outer circumferential end of thewound PSA sheet is mounted to the chuck of the tester and pulled at arate of 300 mm/min to unwind the PSA sheet roll in the tangentialdirection. The unwinding force during this can be converted to anddetermined as the value per width (e.g. 150 mm) of PSA layer of the PSAsheet (N/150 mm). For instance, a preferable PSA sheet roll has anunwinding force of about 0.5 N/150 mm to 2.5 N/150 mm.

The PSA (e.g. PSA layer) constituting the dirt-collecting member (e.g.PSA sheet) is not particularly limited as long as it satisfies the peelstrength to SUS. For instance, the PSA may be formed from an aqueous PSAcomposition such as a water-soluble PSA composition, water-dispersed PSAcomposition and the like or from a PSA composition such as asolvent-based PSA composition and the like. A solvent-free PSA formedfrom an active energy ray-curable PSA composition or a hot melt PSAcomposition can be preferably used as well. To remove human sebum dirt,a solvent-based PSA and solvent-free PSA are preferable. From thestandpoint of the handling, a hot melt PSA is preferable.

The PSA can be an acrylic PSA, rubber-based PSA (e.g. naturalrubber-based PSA), urethane-based PSA, silicone-based PSA, etc. From thestandpoint of the adhesive properties and cost, a rubber-based PSA or anacrylic PSA can be preferably used.

In particular, from the standpoint of controlling the adhesive strength(ease of release), the PSA is preferably an acrylic PSA comprising anacrylic polymer as a base polymer (primary component among polymers, aprimary adhesive component). The acrylic polymer can be synthesized fromstarting monomer(s) comprising, as the primary monomer, an alkyl(meth)acrylate having an alkyl group. The primary monomer herein refersto a monomer that accounts for 50% by mass or more of all the monomers.In the present description, the term “(meth)acrylate” comprehensivelymeans acrylate and methacrylate. Similarly, the terms “(meth)acryloyl”and “(meth)acryl” comprehensively mean acryloyl and methacryloyl, andacryl and methacryl, respectively.

As the alkyl (meth)acrylate, for instance, a compound represented by aformula can be preferably used:

CH₂═CR¹COOR²

Herein, R¹ in the formula is a hydrogen atom or a methyl group. R² is analkyl group having 1 to 20 carbon atoms (hereinafter, such a range ofthe number of carbon atoms may be indicated as “C₁₋₂₀”). From thestandpoint of the storage elastic modulus of the PSA, etc., an alkyl(meth)acrylate having a C₁₋₁₄ (e.g., C₁₋₁₀) alkyl group is preferable.The alkyl group may be linear or branched.

Examples of the alkyl (meth)acrylate having a C₁₋₂₀ alkyl group includemethyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl(meth)acrylate, isoamyl (meth)acrylate, neopentyl (meth)acrylate, hexyl(meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate,isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate,bornyl (meth)acrylate, isobornyl (meth)acrylate, undecyl (meth)acrylate,dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl(meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate,heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl(meth)acrylate and eicosyl (meth)acrylate. These alkyl (meth)acrylatesmay be used singly as one species or in a combination of two or morespecies. In particular, an alkyl (meth)acrylate having a C₄₋₉ alkylgroup is preferable. Preferable examples include n-butyl acrylate (BA),2-ethylhexyl acrylate (2EHA) and isononyl acrylate. Among these, BA and2EHA are more preferable.

The ratio of primary monomer to all the monomers is preferably 60% bymass or higher, more preferably 80% by mass or higher, or yet morepreferably 90% by mass or higher. The upper Emit of the primary monomerratio is not particularly limited. It is preferably 99% by mass or less(e.g. 98% by mass or less, typically 95% by mass or less). The acrylicpolymer can be a polymerization product of essentially just the primarymonomer.

To improve various properties such as the ease of release, etc., thestarting monomers used in polymerization of the acrylic polymer maycomprise, in addition to the primary monomer, a secondary monomer thatcan be copolymerized with the primary monomer. The secondary monomerencompasses not only a monomer, but also an oligomer. As such asecondary monomer, a monomer having a functional group (or “functionalgroup-containing monomer” hereinafter) can be cited. The functionalgroup-containing monomer can be added to incorporate crosslinking pointsinto the acrylic polymer to increase the cohesive strength thereof.Examples of such a functional group-containing monomer includecarboxyl-group-containing monomers, acid-anhydride-group-containingmonomers, hydroxyl-group-containing monomers, amide-group-containingmonomers, amino-group-containing monomers, epoxy-group (glycidylgroup)-containing monomers, alkoxy-group-containing monomers, andalkoxysilyl-group-containing monomers. These can be used as a singlekind alone, or in combination of two or more kinds. Among these,functional group-containing monomers having a functional group ofcarboxyl group, hydroxyl group, epoxy group, etc. are more preferable,and carboxyl-group-containing monomers and hydroxyl-group-containingmonomers are yet more preferable because they can preferably introducecrosslinking points into the acrylic polymer and achieve an even highercohesive strength in the acrylic polymer.

Examples of a carboxyl-group-containing monomer include ethylenicunsaturated monocarboxylic acids such as acrylic acid, methacrylic acid,crotonic acid, carboxyethyl (meth)acrylate, carboxypentyl(meth)acrylate, etc.; ethylenic unsaturated dicarboxylic acids such asitaconic acid, maleic acid, fumaric acid, citraconic acid, etc.; and thelike. Among these, acrylic acid and/or methacrylic acid are preferable,and acrylic acid is especially preferable.

Examples of an acid-anhydride-group-containing monomers include acidanhydrides of the ethylenic unsaturated dicarboxylic acids listed abovesuch as maleic acid anhydride, itaconic acid anhydride, etc.; and thelike.

Examples of a hydroxyl-group-containing monomer include hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc.; unsaturatedalcohols such as N-methylol(meth)acrylamide, vinyl alcohol, allylalcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether,diethylene glycol monovinyl ether, etc.; and the like.

Examples of an amide-group-containing monomer include (meth)acrylamide,N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide,N-methylol(meth)acrylamide, N-methylolpropane(meth)acrylamide,N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, and thelike.

Examples of an amino-group-containing monomer include aminoethyl(meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, t-butylaminoethyl(meth)acrylate, and the like.

Examples of an epoxy-group (glycidyl group)-containing monomer includeglycidyl (meth)acrylate, methylglycidyl (meth)acrylate, allyl glycidylether, and the like.

Examples of an alkoxy-group-containing monomer include methoxyethyl(meth)acrylate, ethoxyethyl (meth)acrylate, and the like.

Examples of an alkoxysilyl-group-containing monomer include3-(meth)acryloxypropyltrimethoxysilane,3-(meth)acryloxypropyltriethoxysilane,3-(meth)acryloxypropylmethyldimethoxysilane,3-(meth)acryloxypropylmethyldiethoxysilane, and the like.

When an aforementioned functional group-containing monomer is used as amonomer constituting the acrylic polymer, the functionalgroup-containing monomer (preferably a carboxyl group-containingmonomer) is preferably added at 1 to 10% by mass (e.g., 2 to 8% by mass,typically 3 to 7% by mass) of all the monomers.

To increase the cohesive strength of the acrylic polymer, etc., anothermonomer besides the functional-group-containing monomer can be includedas a secondary monomer. Examples of such a monomer includevinyl-ester-based monomers such as vinyl acetate, vinyl propionate,etc.; aromatic vinyl compounds such as styrene, substituted styrenes(α-methylstyrene, etc.), vinyl toluene, etc.; and the like.

The method for polymerizing the monomer or a monomer mixture is notparticularly limited, and a general polymerization method heretoforeknown can be employed. Examples of such a polymerization method includesolution polymerization, emulsion polymerization, bulk polymerization,and suspension polymerization. Among these, solution polymerization ispreferable. The embodiment of the polymerization is not particularlylimited and can be carried out with suitable selection of a heretoforeknown monomer supply method, polymerization conditions (temperature,time, pressure, etc.), and other components (polymerization initiator,surfactant, etc.) used besides the monomer. For instance, as the monomersupply method, the monomer mixture can be supplied to a reaction vesselall at once (all-at-once supply), or gradually supplied dropwise(continuous supply), or the mixture can be divided in several portionsand each portion can be supplied at a prescribed time interval(portionwise supply). The monomer or the monomer mixture can be suppliedas a solution or a dispersion containing part or all thereof dissolvedin a solvent or emulsified in water.

The polymerization initiator is not particularly limited. Examplesinclude azo-based initiators such as 2,2′-azobisisobutylonitrile, etc.;peroxide-based initiators such as benzoyl peroxide, etc.; substitutedethane-based initiators such as phenyl-substituted ethane, etc.;redox-based initiators combining a peroxide and a reducing agent such asa combination of a peroxide and sodium ascorbate, etc.; and the like.The amount of polymerization initiator used can be suitably selected inaccordance with the type of polymerization initiator, types of monomers(composition of the monomer mixture) and so on. It is usually suitablyselected from a range of, for instance, about 0.005 to 1 part by mass,relative to 100 parts by mass of all the monomers. The polymerizationtemperature can be, for example, around 20° C. to 100° C. (typically 40°C. to 80° C.).

A crosslinking agent is preferably added to the PSA composition.Preferable examples of a crosslinking agent for an acrylic PSA includeorganometallic salts such as zinc stearate, barium stearate, etc.;epoxy-based crosslinking agents; isocyanate-based crosslinking agents;and the like. Oxazoline-based crosslinking agents, aziridine-basedcrosslinking agents, metal-chelate-based crosslinking agents, andmelamine-based crosslinking agents can also be used. These crosslinkingagents can be used singly as one species or as two or more speciestogether. Among these, epoxy-based crosslinking agents andisocyanate-based crosslinking agents are preferable because they can bepreferably crosslinked to carboxyl groups and are likely to produce goodmaneuverability (typically easy-release nature) and even good acidresistance as well. Combined use of an epoxy-based crosslinking agentand an isocyanate-based crosslinking agent is particularly preferable.The amount of crosslinking agent added is not particularly limited. Inorder to achieve the adhesive strength in the preferable numerical valuerange, it can be about 0.01 to 10 parts by mass (e.g. 0.05 to 5 parts bymass, typically 0.1 to 5 parts by mass) relative to 100 parts by mass ofthe base polymer (e.g. an acrylic polymer). When an epoxy-basedcrosslinking agent (C_(E)) and an isocyanate-based crosslinking agent(C_(I)) are used together, their mass ratio value (C_(E)/C_(I)) ispreferably 0.01 to 1 (e.g. 0.05 to 0.5, typically 0.1 to 0.4).

When a solvent-based PSA is used, preferable examples of a solvent foruse include aliphatic hydrocarbons such as hexane, heptane, mineralspirit, etc.; alicyclic hydrocarbons such as cyclohexane, etc.; aromatichydrocarbons such as toluene, xylene, solvent naphtha, tetralin,dipentene, etc.; alcohols such as butyl alcohol, isobutyl alcohol,cyclohexyl alcohol, 2-methylcyclohexyl alcohol, tridecyl alcohol, etc.;esters such as methyl acetate, ethyl acetate, isopropyl acetate, butylacetate, etc.; ketones such as acetone, methyl ethyl ketone, etc.

The molecular weight (Mw: weight average molecular weight) of the basepolymer (e.g. an acrylic polymer) to be used (synthesized) is notparticularly limited, but a polymer (e.g., an acrylic polymer) having aweight average molecular weight (Mw) of approximately 30×10⁴ to 100×10⁴can be used preferably.

The acrylic polymer constituting the PSA in the art disclosed herein canbe a thermoplastic polymer. A typical example thereof is an acrylicblock copolymer. Can be preferably used an acrylic block copolymercomprising at least one acrylate block (which hereinafter may bereferred to as an Ac block) and at least one methacrylate block (whichhereinafter may be referred to as an MAc block). For instance,preferable is a block copolymer having a structure in which Ac blocksand MAc blocks are positioned alternately. The total number of Ac blocksand MAc blocks is preferably 3 or larger (e.g., 3 to 5).

In typical, the Ac block preferably comprises an alkyl acrylate as theprimary monomer (i.e. the component that accounts for 50% by mass ormore among the block-constituting monomeric units). Of the monomericunits, 75% by mass or more (e.g. 90% by mass or more) can be an alkylacrylate. In a preferable embodiment, the monomeric units constitutingthe Ac block in the acrylic block copolymer (in an acrylic blockcopolymer comprising two or more Ac blocks, possibly at least one of theAc blocks or all the Ac blocks) essentially consist of one, two or morespecies (typically one species) of alkyl acrylate. Alternatively, the Acblock may be a copolymer of an alkyl acrylate and another monomer (e.g.an alkyl methacrylate, etc.).

Examples of the Ac block-constituting alkyl acrylate include methylacrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butylacrylate (BA), isobutyl acrylate, tert-butyl acrylate, n-pentylacrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate,2-ethylhexyl acrylate (2EHA), nonyl acrylate, isononyl acrylate, decylacrylate, dodecyl acrylate, stearyl acrylate, etc. For example, aconstitution where the Ac block-constituting monomers essentiallyconsist of BA alone, 2EHA alone, or both BA and 2EHA can be preferablyused.

It is typically preferable that the MAc block comprises an alkylmethacrylate as the primary monomer. Of all the monomers constitutingthe MAc, 75% by mass or more (e.g. 90% by mass or more) can be an alkylmethacrylate. In a preferable embodiment, the monomeric unitsconstituting the MAc block (in an acrylic block copolymer comprising twoor more MAc blocks, possibly at least one of the MAc blocks or all theMAc blocks) contained in the acrylic block copolymer essentially consistof only one, two or more species (typically one species) of alkylmethacrylate. Alternatively, the MAc block may be a copolymer of analkyl methacrylate and another monomer (e.g., an alkyl acrylate).

The alkyl methacrylate constituting the MAc block may be an alkylmethacrylate whose alkyl group has 1 to 20 (preferably 1 to 14) carbonatoms. Specific examples thereof include methyl methacrylate, ethylmethacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butylmethacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentylmethacrylate, n-hexyl methacrylate, n-heptyl methacrylate, n-octylmethacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, isononylmethacrylate, decyl methacrylate, dodecyl methacrylate, stearylmethacrylate, etc.

In a preferable embodiment, of the monomers constituting the MAc block,50% by mass or greater (or 75% by mass or greater, or essentially all)is an alkyl methacrylate having an alkyl group with 1 to 4 carbon atoms.Especially preferable alkyl methacrylates include methyl methacrylate(MMA) and ethyl methacrylate (EMA). For example, the monomers preferablyemployed may consist essentially of MMA alone, EMA alone, both MMA andEMA, or the like.

The acrylic block copolymer in the art disclosed herein may be acopolymer comprising A blocks and B blocks positioned alternately suchas type AB, type ABA, type ABAB, type ABABA, etc., with the A blockhaving been formed of a polymer having a rigid structure with excellentcohesive strength and elasticity, and the B block having been formed ofa polymer having a flexible structure with excellent viscosity. A PSAcomprising as its base polymer an acrylic block copolymer having such astructure may form a PSA layer combining cohesive strength andelasticity as well as viscosity at high levels. A PSA having such acomposition can be preferably used as a hot melt PSA. An acrylic blockcopolymer (such as type ABA, type ABABA, etc.) having a structure with Ablocks at both termini of the molecule can be preferably used. Anacrylic block copolymer having such a structure is preferable because itis likely to have a good balance of cohesion and thermoplasticity.

When the acrylic block copolymer comprises two or more A blocks, thecompositions, molecular weights (polymerization degrees), structures,etc., of these A blocks can be the same with or different from eachother. When the acrylic block copolymer comprises two or more B blocks,the same is true with the B blocks.

As the A Nock, can be preferably used an MAc Nock as those describedabove. As the B block, can be preferably used an Ac block as thosedescribed above. In a preferable embodiment, the acrylic block copolymeris a triblock copolymer having a structure of MAc-Ac-MAc (type ABA). Forinstance, can be preferably used a triblock copolymer with two MAcblocks having essentially identical monomer compositions.

The ratio of mass of MAc block (when two or more MAc blocks arecontained, their total mass) to mass of Ac block (when two or more Acblocks are contained, their total mass) in the acrylic block copolymeris not particularly limited, but can be preferably in a range such thatthe mass ratio MAc block/Ac block is 4/96 to 90/10 (usually 7/93 to80/20, preferably 10/90 to 70/30, e.g., 20/80 to 50/50). At a large MAcblock ratio, there is a tendency for reduced adhesive strength, allowingfor easy release. At a large Ac block ratio, there is a tendency for anincreased organic dirt-collecting ability.

As the acrylic block copolymer, in usual, can be suitably used anacrylic block copolymer having a weight average molecular weight (Mw) ofabout 3×10⁴ to 30×10⁴. The acrylic block copolymer has a Mw ofpreferably about 3.5×10⁴ to 25×10⁴ or more preferably about 4×10⁴ to20×10⁴ (e.g., 5×10⁴ to 15×10⁴). Too small a Mw of the acrylic blockcopolymer may decrease the adhesive properties (e.g., cohesion) or lowerthe ease of release. Too large a Mw tends to lead to insufficientthermoplasticity of the acrylic block copolymer. The Mw of the acrylicblock copolymer described here refers to a value based on standardpolystyrene that is determined by gel permeation chromatography (GPC)with respect to a sample prepared by dissolving the copolymer in asuitable solvent (e.g., tetrahydrofuran (THF)).

In the acrylic block copolymer in the art disclosed herein, a monomer(other monomer) other than an alkyl acrylate and an alkyl methacrylatemay be copolymerized. Examples of the other monomer include vinylcompounds having functional groups such as alkoxyl group, epoxy group,hydroxyl group, amino group, amide group, cyano group, carboxyl group,acid anhydride group, etc.; vinyl esters such as vinyl acetate; aromaticvinyl compounds such as styrene; vinyl group-containing heterocycliccompounds such as N-vinylpyrrolidone and the like. Alternatively, it canbe an alkyl acrylate having a structure with an acryloyl group coupledto a fluorinated alkyl group, a fluorinated alkyl acrylate and afluorinated alkyl methacrylate. The other monomer may be used, forinstance, to adjust the properties (adhesive properties, ease ofmolding, etc.) of the PSA layer and its content is suitably 20% by massor less (e.g. 10% by mass or less, typically 5% by mass or less) of allthe monomers constituting the acrylic block copolymer. In a preferableembodiment, the acrylic block copolymer is essentially free of the othermonomers.

Such an acrylic block copolymer can be readily synthesized by a knownmethod (e.g. see JP2001-234146, JPH11-323072), or a commercial productis readily available. Examples of the commercial product include tradename “LA POLYMER” series (e.g., those with product numbers LA2140e,LA2250, etc.) available from Kraray Co., Ltd., trade name “NABSTAR”available from Kaneka Corporation, and the like. As the method forsynthesizing the acrylic block copolymer, living polymerization can bepreferably employed. According to living polymerization, while keepingthe weatherability inherent in the acrylic polymer, because of theexcellent structure control unique to the living polymerization, anacrylic block copolymer having excellent thermoplasticity can besynthesized. Since the molecular weight distribution can be controlledin a narrow range, insufficient cohesion caused by the presence of lowmolecular weight components can be reduced to obtain an easilyreleasable PSA (even a PSA sheet (dirt-collecting member)).

When the PSA (e.g. PSA layer) in the art disclosed herein comprises anacrylic block copolymer, solely one species or a combination of two ormore species of acrylic block copolymer can be used. In addition to theacrylic block copolymer, to control the adhesive properties, etc., itmay comprise, as an optional component, a component other than anacrylic block copolymer. Examples of the optional component include apolymer and an oligomer excluding acrylic block copolymers. The amountof the polymer or oligomer (or “optional polymer” hereinafter) issuitably 50 parts by mass or less relative to 100 parts by mass of theacrylic block copolymer, preferably 10 parts by mass or smaller, or morepreferably 5 parts by mass or smaller. In a preferable embodiment, thePSA layer may be essentially free of polymers other than the acrylicblock copolymer.

The PSA composition in the art disclosed herein preferably comprises aplasticizer. The inclusion of plasticizer increases the ease of release.It also lowers the viscosity of the composition and thus the applicationis further facilitated. In yet another aspect, the inclusion ofplasticizer also increases the organic dirt-collecting ability on thePSA surface. The organic dirt collected on the PSA surface is absorbedinto the PSA (e.g. PSA layer) and dispersed therein. Thus, even when thedirt-collecting ability is reduced by repeated use, the dirt-collectingability recovers in relatively short time (e.g. several minutes orseveral hours) as a unique effect (dirt-collecting ability recoveryeffect).

The dirt-collecting ability recovery effect is described with referenceto FIG. 5. As schematically illustrated in FIG. 5, when the PSA layer 32in dirt-collecting member (PSA sheet) 31 is allowed to make contact witha flat surface 2 of an article 1 such as a portable device, etc., thePSA layer 32 collects organic dirt 50 adsorbed on the surface 2. The PSAlayer 32 has a property to not only collect organic dirt 50, but alsocauses it to migrate into the layer. Thus, the organic dirt 50 caught onthe surface of PSA layer 32 migrates with time into the PSA layer 32,leading to a lower presence of organic dirt 50 on the surface of PSAlayer 32; and eventually, the surface of PSA layer 32 will beessentially free of the presence of organic dirt 50. In other words, thesurface regains the same state as before the sticky cleaner is used.Accordingly, the term “recovery effect” refers to an effect such thatwhen the PSA collects organic dirt and the dirt-collecting ability istemporarily reduced, the dirt-collecting ability recovers in aprescribed time period (e.g. several minutes, preferably several hours)and the PSA (e.g. PSA layer) regains the ability to collect dirt. Itencompasses that the dirt-collecting ability requires short time forrecovery.

Examples of plasticizer include phthalic acid esters such as dioctylphthalate, diisononyl phthalate, diisodecyl phthalate, dibutylphthalate, etc.; adipic acid esters such as dioctyl adipate, diisononyladipate, etc.; trimellitic acid esters such as trioctyl trimellitate,etc.; sebacic acid esters; and the like. Softeners such as processed oilare also included in the plasticizer. These can be used singly as onespecies or in a combination of two or more species. Among them, adipicacid esters are preferable.

The amount of plasticizer added is not particularly limited. Forinstance, it is suitably 1 part by mass or greater to 100 parts by massof the base polymer (e.g. an acrylic polymer). The amount added ispreferably 5 parts by mass or greater, more preferably 10 parts by massor greater, yet more preferably 15 parts by mass or greater, orparticularly preferably 20 parts by mass or greater. The amount added issuitably 100 parts by mass or less, preferably 80 parts by mass or less,more preferably 70 parts by mass or less, yet more preferably 60 partsby mass or less, or particularly preferably 50 parts by mass or less.From the standpoint of balancing the dirt-collecting ability anddirt-collecting ability recovery effect, the amount of plasticizer addedis preferably 40 parts by mass or less (e.g. 20 to 40 parts by mass,typically 25 to 35 parts by mass) to 100 parts by mass of the basepolymer.

The PSA composition (or PSA, PSA layer) in the art disclosed herein caninclude, as other components, various additives known in the PSA field,such as tackifier, surfactant, chain transfer agent, anti-aging agent,antioxidant, UV ray absorber, photostabilizer, antistatic agent,colorant (pigment, dye, etc.) and so on. The types and amounts of thesenon-essential additives can be the same as usual types and amounts inthis type of PSA.

When the PSA (e.g. PSA layer) is formed from the PSA compositiondisclosed herein, the formation method is not particularly limited. Forinstance, it is possible to apply a method where the PSA composition isdirectly provided (typically applied) to a substrate, using a heretoforeknown application means such as die coater, gravure roll coater and thelike, and allowed to dry.

The thickness of the PSA layer can be suitably selected in accordancewith the purpose and is not particularly limited. From the standpointsof making sufficient use of the dirt-collecting ability and increasingthe recovery of the dirt-collecting ability, the thickness of the PSAlayer is preferably about 10 μm or larger (e.g. 30 μm or larger,typically 50 μm or larger). When it is important to reduce the weight orsize, etc., the thickness of the PSA layer is preferably 300 μm orsmaller (e.g. 100 μm or smaller, typically 70 μm or smaller). The PSAlayer may be formed entirely over one face of the support substrate.Alternatively, for instance, a non-sticky region (dry edge) free of thePSA layer may be included along each edge of the support substrate'swidth direction.

When the dirt-collecting member disclosed herein comprises a supportsubstrate as in this embodiment, as the support substrate, materialsformed with various types of synthetic resin, non-woven fabric or papercan be used. The material of the support substrate can be a fabric,rubber sheet, foam sheet, metal foil, a composite of these, etc.

Examples of synthetic resin include a polyolefin (polyethylene,polypropylene, ethylene-propylene copolymers, etc.), polyester(polyethylene terephthalate, etc.), vinyl chloride resin, vinyl acetateresin, polyimide resin, polyamide resin, fluorocarbon resin, and theEke. In particular, a support substrate made of polyethyleneterephthalate (PET) can be preferably used. Examples of paper includeWashi, kraft paper, glassine paper, high-grade paper, synthetic paper,top-coated paper, and the Eke. Examples of a fabric include a wovenfabric and a non-woven fabric of a single species or a blend, etc., ofvarious fibrous substances. Examples of the fibrous substance includecotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyesterfiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, andthe like. Examples of a rubber sheet include a natural rubber sheet, abutyl rubber sheet, and the Eke. Examples of a foam sheet include apolyurethane foam sheet, a polychloroprene rubber foam sheet, and thelike. Examples of metal foil include aluminum foil, copper foil, and thelike. The support substrate may contain as necessary various additivessuch as filler (inorganic filler, organic filler, etc.), anti-agingagent, antioxidant, UV ray absorber, photostabilizer, anti-static agent,lubricant, plasticizer, colorant (pigment, dye, etc.), and the like.

When the dirt-collecting member is a single-faced PSA sheet having a PSAlayer formed on a single face of a support substrate, the back face (PSAlayer-free face) of the support substrate is preferably subjected to asurface treatment such as coating of a silicone-based release agent andthe like to adjust the unwinding force of the PSA sheet roll to asuitable range (typically a release treatment to prevent the unwindingforce from becoming excessively high).

The thickness of the support substrate can be suitably selected inaccordance with the purpose and is not particularly limited. In general,the thickness is preferably about 20 μm or larger (e.g. 30 μm or larger,typically 40 μm or larger), but suitably about 200 μm or smaller (e.g.100 μm or smaller, typically 70 μm or smaller).

Several working examples related to the present invention are describedbelow although the present invention is not to be limited to thesespecific examples. In the following explanation, the terms “parts” and“%” are based on the mass unless specifically stated otherwise.

Example 1

To a three-neck flask, were placed 2-ethylhexyl acrylate (2EHA) andacrylic acid (AA) at a mass ratio 2EHA:AA=95:5. Toluene was used as thesolvent. Under a nitrogen flow, benzoyl peroxide was added as apolymerization initiator. The reaction mixture was heated to 60° C. andthe reaction was carried out for 2 hours. The reaction mixture wasfurther heated to 80° C. and the reaction was carried out for 1 hour toprepare a solution of an acrylic polymer A having a weight averagemolecular weight (Mw) of about 50×10⁴ to 60×10⁴. Subsequently, to 100parts of polymeric non-volatiles of the acrylic polymer solution, weremixed 30 parts of a plasticizer (diisononyl adipate “MONOCIZER W-242”available from DIC Corporation), 0.1 part of an epoxy-based crosslinkingagent (“TETRAD-C” available from Mitsubishi Gas Chemical Inc.) and 2parts of an isocyanate-based crosslinking agent (“CORONATE L” availablefrom Nippon Polyurethane Industry Co., Ltd.) to prepare an acrylic PSAcomposition.

The resulting acrylic PSA composition was applied to a surface of a 38μm thick PET support substrate sheet (width: approximately 8 cm) andallowed to dry to fabricate a single-faced PSA sheet having a PSA layerof about 80 μm in thickness (adhesive thickness) formed on the singleface of the support substrate. The resulting single-faced PSA sheet waswound around the surface of a drum-shaped holding member (20 mmdiameter) to form a PSA sheet roll. The holding member was installed onan end of a grip member in a freely rotatable (rolling) manner toconstruct a cleaner as schematically shown in FIGS. 1 and 2.

Example 2

The amount of epoxy-based crosslinking agent was increased to 0.5 partrelative to 100 parts of polymeric non-volatiles of the acrylic polymersolution. Otherwise, in the same manner as Example 1, a cleaneraccording to Example 2 was constructed.

Example 3

The amount of plasticizer added was increased to 60 parts relative to100 parts of polymeric non-volatiles of the acrylic polymer solution.Otherwise, in the same manner as Example 2, a cleaner according toExample 3 was constructed.

Example 4

Were mixed 100 parts (non-volatiles) of a commercial acrylic Nockcopolymer (acrylic polymer B) and 30 parts of a plasticizer (diisononyladipate “MONOCIZER W-242” available from DIC Corporation) to prepare ahot melt acrylic PSA. The resulting acrylic PSA was melted and appliedto a surface of a 38 μm thick PET support substrate sheet (width:approximately 8 cm) to fabricate a single-faced PSA sheet having a PSAlayer of about 50 μm in thickness (adhesive thickness) formed on thesupport substrate. Using the resulting single-faced PSA sheet, otherwisein the same manner as Example 1, a cleaner according to Example 4 wasconstructed.

Example 5

The amount of plasticizer added was increased to 100 parts relative to100 parts (non-volatiles) of the acrylic Nock copolymer. Otherwise, inthe same manner as Example 4, a cleaner according to Example 5 wasconstructed.

Example 6

A commercial roller floor cleaner (trade name “COLOCOLO” available fromNitoms, Inc.) was used as Example 6.

[Measurement of 180° Peel Strength to SUS]

The PSA sheet according to each example was cut to 200 mm by 25 mm toobtain a rectangular test piece. The test piece was adhered over thesticky surface (PSA layer-side surface) to a stainless steel (SUS304)plate with a 2 kg roller moved back and forth once. The resultant wasstored in an environment at 23° C. and 50% RH for 30 minutes. Based onJIS Z0237, using a tensile tester, in an environment at 23° C. and 50%RH, the 180° peel strength (N/25 mm) to SUS was measured at a peel angleof 180° and at a tensile speed of 300 mm/min. Measurements were madewith “TENSILON” available from Shimadzu Corporation. The results areshown in Table 1.

[Measurement of 180° Peel Strength to Glass]

With respect to the PSA sheets according to Examples 1 to 3, using aglass plate as the adherend, otherwise in the same manner as the 180°peel strength to SUS, the 180° peel strength (N/25 mm) to glass wasmeasured. As the glass plate, a commercial float glass plate was used.The results are shown in Table 1.

[Measurement of 180° Peel Strength to PET]

With respect to the PSA sheets according to Examples 1 to 3, using a PETfilm (50 μm thick) as the adherend, otherwise in the same manner as the180° peel strength to SUS, the 180° peel strength (N/25 mm) to PET wasmeasured. The results are shown in Table 1.

[Assessment of Dirt Removal Rate]

A tablet terminal (iPad®, a product of Apple Inc.) was obtained and thedisplay (flat surface made of aluminosilicate glass) was thoroughlycleaned with each cleaner and subjected to a measurement of gloss valueG0 (60° measurement angle), using a handy gloss meter “Gloss CheckerIG-331” available from Horiba, Ltd. Subsequently, sebum on the tester'sface and other body skin was rubbed on fingers and the organic sebumdirt on the fingers was rubbed on and transferred to an area of thedisplay of the tablet terminal. The organic dirt was transferred in anamount to yield a gloss value of about 60 (G1). The display's surfacehaving the sebum dirt was cleaned with the cleaner according to eachexample. In particular, the PSA sheet roll of the cleaner according toeach example was allowed to rotate once. The rolling speed was about 0.5msec. The pressure applied by the operator for the rotation was about700 g. The display was then subjected to a measurement of gloss value G2(60° measurement angle) to determine the dirt removal rate (%) based onan equation: dirt removal rate (%)=(G2−G1)/(G0−G1)×100. Two measurementswere taken and their average value was recorded. The results are shownin Table 1.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Composition (parts) Acrylicpolymer A 100 100 100 — — — Acrylic polymer B — — — 100 100 Plasticizer30 30 60 30 100 Epoxy-based crosslinking agent 0.1 0.5 0.5 — —Isocyanate-based crosslinking agent 2 2 2 — — 180° Peel strength (N/25mm) To SUS 0.80 0.16 0.09 0.04 0.02 9.7 To Glass 0.82 0.11 0.06 — — — ToPET 0.36 0.08 0.02 — — — Dirt removal rate (%) 100 99 99 100 93 89

As shown in Table 1, the cleaners according to Examples 1 to 5 wereeasily releasable, exhibiting adhesive strengths of less than 1 N/25 mmas measured values based on the 180° peel test specified in JIS Z0237.Despite the easy-release nature as described above, the cleanersaccording to these examples achieved greater organic dirt-removingabilities than the cleaner according to Example 6 having relativelystrong adhesive strength. Similarly to usual dirt, at least a certainadhesive strength has been considered necessary also with respect toorganic dirt such as human sebum dirt and the like. It has beenvalidated, however, that even a PSA as poorly adhesive as the PSA sheetsof the respective examples can even exhibit sufficient dirt-removingabilities. This has been revealed for the first time through the studiesby the present inventors. For instance, even on a portable devicesurface covered with removable protection film, because of theeasy-release nature, a sticky cleaner as easily releasable as thosedescribed above can be expected to clean the surface (in this case, thesurface of the protection film) without removing the protection film. Aperson skilled in the art would recognize this because of the low peelstrength to PET which is a synthetic resin.

Although specific embodiments of the present invention have beendescribed in detail above, these are merely for illustrations and do notlimit the scope of claims. The art according to the claims includesvarious modifications and changes made to the specific embodimentsillustrated above.

REFERENCE SIGNS LIST

-   1 portable device (article)-   2 surface (display)-   10 sticky cleaner-   20 holding member-   30 PSA sheet roll-   31 PSA sheet (dirt-collecting member)-   32 PSA layer-   36 substrate-   40 grip member-   42 handle-   50 organic dirt

1. A sticky cleaner used for removing organic dirt adsorbed on a surfaceof an article, the sticky cleaner comprising a dirt-collector thatcollects the organic dirt as the dirt-collector makes contact with thesurface of the article, the dirt-collector has a surface-contacting partto make contact with the surface of the article, the surface-contactingpart being formed with a pressure-sensitive adhesive, and thesurface-contacting part of the dirt-collector exhibits an adhesivestrength of less than 1 N/25 mm as a measured value based on the 180°peel test specified by JIS Z0237.
 2. The sticky cleaner according toclaim 1, wherein the surface-contacting part of the dirt-collectorexhibits an adhesive strength of 0.01 N/25 mm to 0.5 N/25 mm as themeasured value based on the 180° peel test specified in JIS Z0237. 3.The sticky cleaner according to claim 1, wherein the sticky cleanercomprises a cylindrical rolling member, and the dirt-collector isarranged along the lateral surface of the rolling member.
 4. The stickycleaner according to claim 3, further comprising a grip that rotatablysupports the rolling member.
 5. The sticky cleaner according to claim 1,wherein the dirt-collector is an adhesively single-facedpressure-sensitive adhesive sheet comprising a sheet of supportsubstrate and a pressure-sensitive adhesive layer placed above thesupport substrate, and the single-faced pressure-sensitive adhesivesheet is wound with the pressure-sensitive adhesive layer on the outsideto form a pressure-sensitive adhesive sheet roll.
 6. The sticky cleaneraccording to claim 5, wherein the pressure-sensitive adhesive layercomprises an acrylic polymer at a ratio of 50% by mass or higher.
 7. Thesticky cleaner according to claim 6, wherein the acrylic polymer is acrosslinked acrylic polymer.
 8. The sticky cleaner according to claim 6,wherein the acrylic polymer is a thermoplastic acrylic polymer.
 9. Thesticky cleaner according to claim 6, wherein the pressure-sensitiveadhesive layer further comprises a plasticizer.
 10. The sticky cleaneraccording to claim 1 used for removing human sebum dirt as the organicdirt.
 11. The sticky cleaner according to claim 1, wherein the articleis a portable device having a flat surface on which a glass or syntheticresin display is present.